Using two SIM cards with same MSISDN number

ABSTRACT

A method and equipment for using two SIM cards with the same MSISDN number in a mobile communication system. To at least one subscriber identifier are allocated at least two identity modules (SIM), of which only one at a time can be registered as active. In connection with location updating it is checked whether the location updating relates to a subscriber identifier to which at least two identity modules (SIM) have been allocated. If yes, it is checked whether the identity module (SIM) concerned is at that particular moment registered as passive, and if yes, it is activated 3and the identity module (SIM) earlier registered as active is deactivated. If the identity module (SIM) earlier registered as active is involved in an on-going call while location updating is being performed using an identity module (SIM) earlier registered as passive, the location updating is rejected or delayed until the on-going call has been terminated.

This application is the national phase of international applicationPCT/FI97/00714 filed Nov. 24, 1997 which designated the U.S.

FIELD OF THE INVENTION

The invention relates to a method and equipment for using two SIM cardswith the same MSISDN number in a mobile communication system.

BACKGROUND OF THE INVENTION

In order to illustrate the invention, but in no way to restrict it, theinvention is described within a GSM system (Global System for MobileCommunications) and using its terminology. As shown in FIG. 1, thestructure of the GSM network consists of two main parts: a Base StationSubsystem (BSS) and a Network Subsystem (NSS). The BSS and mobilestations MS communicate via radio connections. In the BSS, each cell isserved by a Base Transceiver Station (BTS). A group of base transceiverstations BTS is connected to a Base Station Controller (BSC), thefunction of which is to control the radio frequencies and channels usedby the base transceiver station BTS. The base station controllers BSCare connected to a Mobile Switching Centre (MSC). The function of themobile switching centre is to switch calls involving at least one mobilestation MS. Some MSCs are coupled to other data communication networks,such as a Public Integrated Services Network (PISN), and they compriseswitching functions for processing calls to and from these networks.These mobile switching centres are called Gateway Mobile SwitchingCentres (GMSC or Gateway MSC).

The GSM system has two types of databases for routing calls. Networksubscriber data are stored, permanently or semi-permanently, at a HomeLocation Register (HLR). These data include, for instance, informationabout those services the subscriber has access to and the subscriber'scurrent location. The other register type is a Visitor Location Register(VLR). It is usually connected to a single mobile switching centre MSC,but it can also serve several centres. The Visitor Location Register iscommonly integrated in the mobile switching centre MSC. An integratednetwork element such as this is briefly called a VMSC (Visitor MSC).When the mobile station MS is active (it has registered in the networkand can initiate or receive a call), the majority of the subscriber dataconcerning the mobile station MS in the Home Location Register HLR isloaded (copied) into the Visitor Location Register VLR of the mobileswitching centre MSC in whose area the mobile station MS is located.

Base stations BTS continuously broadcast information about themselvesand their environment. The information comprises e.g. a location areaidentifier, base station identifier, base station type and what is knownas adjacent cell information. When a mobile station MS is locked to thebase station of a specific cell, it also monitors the transmissionquality of the base stations indicated by the adjacent cell informationsent by the base station BTS, and changes over to one of these basestations if the coverage of the current base station degrades. Acellular radio network usually knows the location of a mobile stationwith the accuracy of what is known as a Location Area (LA). A locationarea usually includes a suitable number of predefined cells and theirbase stations. Location area data, for instance a Location Area Index(LAI), sent by a base station informs the mobile station of the locationarea that the base station BTS belongs to. When the mobile station MSchanges cells within the same location area, location updating to thecellular radio network is not needed. But when the mobile stationchanges over to a new base station and notices on the basis of thelocation area data—for instance the LAI—that the location area changes,the mobile station initiates location updating by sending a locationupdate request to the cellular radio network. As a result of thislocation update request the network stores the new location area of themobile station in its subscriber registers. The location updating in theGSM system given as an example is described e.g. in Mouly-Pautet, “TheGSM System for Mobile Communications”, particularly chapter 7.1.4, andin the ETSI recommendation “GSM 03.12, Location Registration ProceduresDCS, ETSI/PT 12”.

FIG. 2 illustrates signalling relating to location updating. In FIG. 2it is assumed, similarly as in the GSM system, that a mobilesubscriber's MSISDN identifier (Mobile Subscriber ISDN) is not used onthe radio path. Instead, an IMSI identifier (International MobileSubscriber Identity) or a TMSI identifier (Temporary Mobile SubscriberIdentity) is used in order to protect the subscriber's identity. In step2-1 the mobile station MS sends a location update requestLoc_Update_Req, which proceeds (via the base station BTS and the basestation controller BSC) to the mobile switching centre MSC. In step 2-2the mobile switching centre MSC sends a location update command to thevisitor location register VLR, which performs the update in step 2-3. Instep 2-4 the visitor location register VLR sends an acknowledgement tothe mobile switching centre MSC to the effect that the location updatinghas been performed, the MSC forwarding the acknowledgementLoc_Update_Ack to the mobile station MS in step 2-5.

The IMSI (or the TMSI) and the mobile subscriber's MSISDN are associatedwith each other in the home location register HLR in a way described forinstance in Mouly-Pautet, “The GSM System for Mobile Communications”,particularly chapter 8.1.1.3. To sum up, the home location registermaintains a conversion table or file associating a specific MSISDNnumber with a specific IMSI number. Table T in FIG. 3 represents thistable.

FIG. 3 illustrates the set-up of a call terminating at a mobile stationMS in a GSM mobile communication system. If the mobile station MS givenin FIG. 1 is not located within the area of its own home locationregister, the parts in FIG. 2 correspond to those in FIG. 1, with thehome location register HLR and the visitor location register VLR being,however, connected to different mobile switching centres MSC. In step3-1 the call arrives at the Gateway Mobile Switching Centre (GMSC),which in step 3-2 defines, on the basis of the directory number MSISDNof the called subscriber, the subscriber's home location register HLRand sends it an inquiry concerning routing information. Informationindicating the visitor location register VLR in the area of which thesubscriber is located has been updated to the subscriber's home locationregister HLR in connection with location updating. In step 3-3, on thebasis of this information, the home location register HLR sends arequest Provide Roaming Number to the visitor location register VLR. Themobile subscriber's IMSI is also sent to the visitor location registerVLR in this request. In step 3-4 the VLR stores the data it has receivedand reserves a Mobile Station Roaming Number (MSRN). In step 3-5 the VLRsends the roaming number MSRN it has reserved to the home locationregister HLR, which in step 3-6 transmits it to the centre GMSC whichinquired the routing information. A roaming number domain is defined insuch a way that a call is always routed to that mobile switching centreMSC whose visitor location register VLR has reserved the roaming numberconcerned. On the basis of the roaming number MSRN, the gateway mobileswitching centre GMSC can thus route the call forward by sending in step3-7 an initial address message to the mobile switching centre MSCindicated by the roaming number MSRN. In this example the mobileswitching centre MSC concludes from the roaming number MSRN that thecall will terminate in the area of its own centre. In step 3-8 themobile switching centre MSC inquires of its own visitor locationregister VLR the called subscriber's information for setting up thecall. In a normal case the visitor location register VLR returns in step3-9 the information needed for setting up the call. Arrows 3-10 and 3-11describe this process.

In the exemplary GSM system, authentication of the mobile subscriberrequires an identity module which is subscriber-specific. A terminalequipment proper is therefore not confined to a specific. subscriber.The subscriber identity module, such as a SIM card (Subscriber IdentityModule), is a functional card or a smart card which is placed in themobile station and which contains information, e.g. an authenticationkey K_(i), needed for identifying a subscriber and for encrypting radiotraffic. In the present application, a subscriber identity module, suchas a SIM card, refers to a functional card that is used in a mobilestation and can usually be removed from it and by means of which thesubscriber is able to use a card controlled mobile station.

In other words, if a subscriber identity module, e.g. a SIM card isused, the user need not necessarily have a mobile station of his own.Instead, it is sufficient that he has a subscriber identity moduleissued by a mobile communication system operator, such as a SIM card,which is, in a way, a phone card and which the subscriber can use formaking and receiving calls from any mobile station in the system. Thefunction of the SIM card is, on the one hand, to offer subscriberidentifying data for the use of the mobile station in a well protectedform and, on the other hand, to provide services for the mobile station.Such services include e.g. maintaining (entering, changing) a personalidentification number, maintaining a data encryption key, i.e.authentication key K_(i), and unblocking a SIM card blocked due to toomany attempts to enter a wrong Personal Identification Number (PIN). Ablocked SIM card is unblocked for instance with a PUK code (PersonalUnblocking Key).

An alternative introduced for implementing a SIM card in hand-heldphones is a component called a plug-in-SIM, which is about the size of acoin and contains the electronics of the SIM card of a credit card size.The plug-in-SIM is inserted into the phone in such a way that it is noteasy for the user to replace it. The phone can also have an incorporatedplug-in-SIM and, in addition, a card reader. When there is a card in thecard reader, the phone is identified on the basis of the external card,otherwise on the basis of the incorporated plug-in-SIM card.

In the present application a Mobile Station (MS) thus consists of twoelements: a Mobile Equipment (ME) and a Subscriber Identity Module(SIM). The SIM card is specified in GSM recommendation 02.17.Recommendation 11.11 specifies in closer detail the matters defined inrecommendation 02.17 by determining for instance the protocols betweenthe SIM and the ME, the exact contents and length of the SIM data fieldsand matters relating to electronic and mechanical interfaces. An exampleof a data field included in the SIM card is IMSI, the number identifyingthe mobile subscriber. Further, in the present application, the conceptSIM refers to a subscriber identity module in general, e.g. to a SIMcard, a small plug-in-SIM card, a SIM smart card of a credit card sizeand a subscriber identity module incorporated into a mobile station andcontaining the subscriber identity and the authentication key K_(i),unless the context gives reason to some other interpretation.

The above described prior art subscriber registration into the system,location updating and call set-up are usually sufficient when a singlesubscriber has one telephone set and one SIM card at a time at hisdisposal. A problem this invention offers a solution for arises when asingle subscriber has two identity modules which he wishes to associatewith the same subscriber number. A situation like this can arise forinstance when the subscriber has two different telephone sets, one ofwhich uses a full size SIM card and the other one a small SIM card. Oneof the telephones can be a pocket-size portable phone which is used inlocations where the network coverage is good. The other can be forinstance a large and high-power telephone equipped with an externalantenna and used in a car or a boat. The subscriber wishes to have a SIMcard for both telephones, but does not want to pay for two separatesubscriptions. Another similar situation arises in countries wherelegislation requires that if an employee has a company telephone at hisdisposal, it should be possible to separate calls made outside theworking hours from those made during the working hours. Usually,however, the subscriber wishes that he can be reached with the samesubscriber number, irrespective of whether he is contacted during oroutside the working hours.

BRIEF DESCRIPTION OF THE INVENTION

The object of the invention is to provide a method and equipmentimplementing the method where a single mobile subscriber can have twodifferent SIM cards of either the same or a different size at hisdisposal; the subscriber can be always reached with the same subscribernumber; the implementation should be as simple, reliable andunnoticeable as possible to the subscriber. The objects of the inventionare achieved with methods and arrangements characterized by what isstated in the independent claims. The dependent claims relate to thepreferred embodiments of the invention.

The invention is based on a mobile telephone network (for instance itshome location register HLR) maintaining information that a subscriberidentifier (an MSISDN number) is associated with two or more SIM cards,of which one at the most, however, is active at a time. (Usually one ofthe SIM cards is active, but when an active SIM card is being changed, atemporary situation where none of the SIM cards is active can arise.)When a mobile station which has a SIM card registered as passiveperforms location updating, the network (for instance the home locationregister HLR) notices that the MSISDN number is associated with two SIMcards, of which the one that is currently passive is performing locationupdating. In this case the network deactivates the SIM card used earlierand activates that SIM card which is used for performing the locationupdating. The operation then continues as normally.

One advantage the method and system of the invention offer is that theyare reliable and unnoticeable to the subscriber. All the subscriber hasto do is to use his telephone. From the subscriber's point of view, theswitch between an active and a passive SIM card takes placeautomatically, without a separate spoken or keyed message to a billingcentre or the like. An implementation according to the invention ispossible irrespective of whether the SIM cards are of the same or adifferent size. A further advantage the method and equipment of theinvention can be considered to have is that the changes can be limitedto a small, clearly defined area in a single network element, mainly insoftware and information elements associated with the home locationregister HLR.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is now described in more detail in connection withpreferred embodiments, and with reference to the attached drawings ofwhich

FIG. 1 is a block diagram showing elements of a mobile telephone networkessential to the invention;

FIG. 2 illustrates signalling relating to location updating:

FIG. 3 illustrates signalling relating to call set-up;

FIG. 4 is a flow diagram illustrating the invention; and

FIGS. 5A-5B show alternative techniques for associating several SIMcards with one and the same subscriber number.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 4 is a flow diagram showing additional operations of the inventionrelating to location updating Receiving an IMSI in connection withlocation updating involves checking whether other IMSI identifiers areassociated with the same subscriber. If yes, then it is checked whetherthe location updating relates to an IMSI identifier registered asactive. If the location updating relates to an IMSI identifierregistered as passive, the IMSI used earlier is deactivated and the IMSIassociated with the location updating is activated.

Referring now to FIG. 5A, in one embodiment of the invention the homelocation register HLR maintains, as described in the invention,information indicating that at least two SIM cards are associated with aparticular MSISDN number. This information can be maintained forinstance by extending the conversion table T described in connectionwith FIG. 3 with an extra information element E in such a way that twoor more IMSI identifiers can be entered in extended table T for eachMSISDN number. It is to be noted in this first embodiment that therecord format of the data file, i.e. of the table T,. changes, which hasto be taken into account when the software processing the tableconcerned is updated. If more than two IMSI identifiers (SIM cards) areto be obtained for each MSISDN number, more than one extra informationcolumn E will naturally be required.

According to this alternative, when the home location register HLRnotices in connection with location updating that the location updatingrelates to an MSISDN number associated with more than one SIM card, theHLR checks whether the SIM card indicated by the location update messageis the one registered as active (i.e. whether the IMSI corresponding tothe SIM card in table T is stored in the first IMSI field). If yes, thenthe location updating proceeds according to prior art. But if the SIMcard indicated by the location update message is not the one registeredas active (i.e. the IMSI corresponding to the SIM card in table T isstored in a field other than the first one), the HLR activates the IMSIindicated by the location update message, for instance by transferringit into the first IMSI field. The SIM card corresponding to this IMSInow becomes active. The IMSI used earlier is deactivated, e.g. bystoring it in the IMSI field just released. The deactivation of the SIMcard used earlier is signalled to the visitor location register VLR forinstance by sending a Mobile Application Part (MAP) message CANCELLOCATION corresponding to the SIM card just deactivated. The visitorlocation register VLR deletes the deactivated SIM card from its memory.This is a standard operation for the visitor location register, so theinvention does not require any changes in the visitor location registerfunctionality.

An alternative for transferring the active IMSI into the first column isto maintain a separate field (not shown) which indicates which one ofthe IMSIs of a particular subscriber is active.

FIG. 5A shows, as an example, an imaginary situation where a second anda fifth subscriber (MSISDN number) are associated with two SIM cards andthus two IMSI identifiers. As regards the second subscriber, SIM card Ais active (IMSI-2A is in the first IMSI field). Correspondingly, asregards the fifth subscriber, SIM card B is active (IMSI-5B is in thefirst IMSI field).

Referring now to FIG. 5B, one alternative embodiment is based on thefact that probably only a small fraction of the subscribers use severalSIM cards. According to this second alternative, several SIM cards canbe associated with one and the same MSISDN number by means of additionalextension table T' which only holds information about MSISDN numberswith more than one associated SIM card. In this embodiment, the recordformat of table T does not change, but all changes are collected intothe separate extension table T'. In certain situations this can beconsidered an advantage. The processing of table T only changes in sucha way that when a SIM card is changed (in connection with locationupdating), the IMSI corresponding to the activated SIM card must becopied into table T.

According to this second alternative, the home location register HLRchecks in connection with location updating whether the MSISDN indicatedby the location updating is stored in extension table T'. If not, thelocation updating continues according to prior art. But if the MSISDNindicated by the location updating is stored in extension table T', theHLR checks whether the SIM card indicated by the location update messageis the one registered as active (i.e. whether the IMSI corresponding tothe SIM card in extension table T' is the same as the one entered intable T). If yes, the location updating continues according to priorart. But if the SIM card indicated by the location update message is notthe one registered as active (i.e. the IMSI corresponding to the SIMcard in extension table T' is not the same as the IMSI entered in actualtable T, the HLR copies the IMSI indicated by the location updatemessage from extension table T' to actual table T. At the same time, aCANCEL LOCATION message is sent to the visitor location register VLRsimilarly as described above in connection with FIG. 5A. The locationupdating then continues according to prior art.

FIG. 5B shows, as an example, an imaginary situation where two SIMcards, and thus two IMSI identifiers, are associated with each MSISDNnumber 2, 41 and 64. For one of the subscribers SIM card A is active(IMSI-2A is stored in table T).

Table T in FIG. 5A or extension table T′ in FIG. 5B can naturally beextended so as to enable even more than two SIM cards (IMSI identifiers)to be associated with a single MSISDN number.

It is possible that two (or more) SIM cards with different subscribersare associated with the same MSISDN number. If a SIM card (e.g. A)earlier registered as active is involved in an ongoing call at the sametime as a SIM card earlier registered as passive (in this case B) isbeing activated (it is being used for performing location updating), thelocation updating concerning the SIM card A is preferably delayed orrejected until the on-going call has been terminated. This kind of asituation can be communicated to the user of SIM card A e.g. with a callwaiting function.

Call information relating to billing is transmitted to the networkbilling centre. The post-processing that takes place there is preferablysupplemented by grouping the invoices in such a way that calls madeusing different SIM cards/IMSI numbers can be separated in them. Ifbilling is controlled on the basis of the IMSI identifier, the extrainformation element E provided by the invention can be used forcombining the different IMSI identifiers associated with one and thesame MSISDN number to form one bill.

It is apparent to a person skilled in the art that, as technologyadvances, the basic idea of the invention can be implemented in manydifferent ways. The above description relates to the GSM system and itsderivatives, such as the DCS, but the invention is applicable to otherdata communication systems as well. For instance, it is not essentialthat the subscriber identity module is a removable GSM type SIM card. Itis conceivable that as mobile stations become smaller, a physicallyremovable SIM card like the current one will not necessarily be used anymore. The division between the mobile equipment ME and the identitymodule SIM can be understood to be more logical than physical. It isalso conceivable that as mobile stations become less expensive, atypical subscriber can have several mobile stations, of which he/sheselects the one best suited to the environment concerned. The art of theinvention can also be applied in a situation like this. An essentialfeature of the invention is that a mobile station comprises a subscriberidentity module and that several identity modules are to be associatedwith one and the same subscriber identifier. The invention and itsembodiments are therefore not restricted to the above examples, but theycan vary within the scope of the claims.

What is claimed is:
 1. A method for mobile station location updating ina cellular mobile communication system having at least one Home LocationRegister and at least one Visitor Location Register, and in which eachsubscriber is associated with a subscriber identifier, and the mobilestation includes a subscriber identity module, the method comprising:allocating at least two identity modules for each at least onesubscriber identifier, each one of the at least two identity moduleshaving an active state and a passive state, each one of the at least twomodules being defined such that, at most, one of the at least twoidentity modules has a subscriber identifier active at any given time;determining whether a subscriber identifier associated with locationupdating has at least two allocated identity modules; if the locationupdating relates to a subscriber identifier to which at least twoidentity modules have been allocated, checking whether an identitymodule allocated to the subscriber identifier is registered as passive;and if the allocated identity module is registered passive, activatingthe allocating identity module and deactivating an identity moduleearlier registered as active.
 2. The method of claim 1, furthercomprising rejecting or delaying the location updating until theon-going call is terminated if the identity module earlier registered asactive is involved in an on-going call at the same time as locationupdating is being performed using an identity module earlier registeredas passive.
 3. The method of claim 2, further comprising communicating asuccessful or an attempted location updating relating to the identitymodule registered as passive during a call to a subscriber of theidentity module earlier registered as active.
 4. A mobile communicationnetwork element including a lookup table for associating an identitymodule with a subscriber identity, the network element comprising: anextra information element within the lookup table configured toassociate at least two identity modules with the same subscriberidentifier for at least one subscriber such that, at most, one identitymodule is registered as active at any given time; and an activationsignal configured to activate an identity module involved in locationupdating and a deactivation signal for deactivating another identitymodule earlier registered as active in response to the location updatingof a subscriber having at least two allocated identity modules.